Magnetic switching devices and systems



Aug. 16, 1960 M. RUBINOFF 2,949,504

MAGNETIC SWITCHING DEVICES AND SYSTEMS Filed Nov. 26. 1958- F/G D H6 2 B INVERTER INPUT OUTPUT c H E O MADE FROM MAGNETIC MATERIAL 0F WASP-WAISTED MAGNETIZATION CLOCK F CHARACTERISTIC PULSE 0R BUFFER 7 Fla 5 JOINT DENIAL GATE la 4 PuLsE\ TELEPHONE CONTROL SWITCHING CIRCUIT F/G. 6

AND GATE INVERTED 3 SIGNAL OUTPUT 9 INVERTED SIGNAL 2 w CLOCK PULSE FIG. 7 TELEPHONE CROSSPOINT Iw SWITCHING CIRCUIT LINE LINE

LINE

IN V EN TOR, MORRIS RUB/NOFF.

41 romv x LINE United States Patent MAGNETIC SWITCHING DEVICES AND SYSTEMS Morris Rubinofi, Sharon Hill, Pa., assignor to the United States of America as represented by the Secretary of the Army Filed Nov. 26, 1958, Ser. No. 776,654

8 Claims. (Cl. 179-15 The invention relates to electrical switching devices and systems and particularly to such devices and systems of the magnetic type for use in telephone or other signal communication systems.

Magnetic switching devices employing for the main switching control elements one or more cores made from a saturable magnetic material and two or more control windings wound on each core have been used previously for control purposes in computer, counting and similar systems because of their many obvious advantages over control devices of other types, such as vacuum tubes, gaseous discharge tubes, diodes, etc. for these purposes. For example, a magnetic core is a passive element of high reliability, considerable ruggedness and indefinite long life, so that it requires relatively little maintenance. Also, the magnetic properties of the magnetic material used in such cores are usually not subject to much variation with temperature; and for most applications the cores require very small dimensions so that their use is desirable in situations where the space problem is an important factor. For the particular switching or control operations required to be performed by these devices in the prior art systems, the magnetic material in the cores is usually selected to possess high retentivity and preferably have magnetization or hysteresis characteristics essentially rectangular in shape, i.e., having residual flux densities which are relatively large percentages of the original flux densities present under applied magnetomotive forces.

A general object of the invention is to improve magnetic switching devices and systems from the standpoint of reduction in initial and maintenance costs.

A related object is to provide a magnetic switching device which will have in addition to the above-mentioned advantages the further advantages of requiring a very small amount of operating power for each core used, and no demagnetizing or standby power.

Another object is to modify the magnetic cores in such switching devices to make their magnetic characteristics more suitable for providing the types of switching control required in an electronic telephone switching office.

Another object is to produce efiiciently and economically difierent types of switching operations required in an automatic telephone switching office with magnetic switching devices utilizing the same type of magnetic material in their cores. 7

These objects are attained in accordance with the invention primarily by the use in the cores of magnetic switching devices and systems of a magnetic material of the type having the so-called wasp-waisted magnetization characteristic, in which the remanent flux density is always very small compared to saturated flux density and the permeability is negligible until a coercive mat netic field above a given strength is applied to cause the permeability of the core material to be increased to a relatively high value. Applicant has found that magnetic material having such a characteristic is particularly suitable for use in magnetic cores to provide the switch- 2,949,504 Patented Aug. 16, 1960 ing control operations required in two major telephone system applications, namely, (1) control switching and (2) crosspoint switching, and has evolved a number of switching devices and systems for providing these operations utilizing magnetic cores made from a magnetic material having this magnetization characteristic.

It is well known that all logical switching circuits can be constructed from inverters and either gates (AND circuits) or buflers (OR circuits).

One switching arrangement in accordance with the invention adapted for use as one component in a magnetic system for producing the control switching operations required in an electronic telephone switching oflice, utilizes a core made from a magnetic material having a wasp-waisted magnetization characteristic and three inductive windings on the core. Such an arrangement can be used as an inverter to give an output signal in a circuit connected to one of the windings when the core material is magnetized under control of a magnetizing or clock pulse applied to a second one of these windings only in the absence of an input signal applied to the third winding.

A feature of this and the other switching devices in accordance with the invention is that the core material returns automatically to the neutral (unmagnetized) condition at the end of each control pulse, whether or not the core has been magnetized to the saturated condition, without the use of any demagnetizing force for accomplishing this and is maintained in this neutral condition without the use of any holding power.

A second switching arrangement in accordance with the invention differs from the first arrangement merely in the provision of one or more additional input windings on the core which with the first input winding may be used for applying two or more input signals thereto any one of which is of sufiicient magnitude to prevent the core from being activated by the clock pulse so that the unit will provide an output signal only in the absence of any input signals. This circuit, therefore, operates as a Joint Denial Gate.

A third switching arrangement in accordance with the invention differs from the second arrangement only in the provision of means for inverting each of the original inputs before they are applied to the core (or the logical equivalent performed earlier in the operation), so that an output signal will be generated in the output circuit only in the presence of a signal in each of the original inputs; i.e., it will operate as an AND gate.

A fourth switching arrangement in accordance with the invention comprises the combination of the abovedescribed joint denial gate and inverter switch arrangements, the single output winding of the former being connected through an intermediate circuit to the single input winding of the inverter. This arrangement will produce a signal output in the output winding of the inverter portion only in the presence of a signal in one or more of the input windings of the associated joint denial gate portion; i.e., it will operate as an OR bufier.

By the use of various combinations of the above-described inverterand gating arrangements employing cores made from magnetic material having a wasp-waisted magnetization characteristic, any desired logical switching operation can be performed. For example, one ar- V 3 cuit and the interconnections between the windings are selected such that when there is a signal in any input, no signals will appear in the output circuit, and when there is no input signal an output signal will be induced in the output circuit. The undesired flow of information backwards along the input lines (i.e., currents induced in the input windings) is eliminated in this arrangement.

Magnetic cores made from magnetic material having a Wasp-waisted magnetization characteristic may also be utilized in accordance with the invention in the crosspoint switches of an electronic telephone switching oflice to control the inter-connection of the voice lines of various pairs of subscribers to enable voice communication between them, on demand of one of these subscribers; and to maintain such a connection as long as desired by the subscribers. Each crosspoint switch would comprise a toroidal core made from material having such characteristics with a two-winding transformer and an auxiliary biasing winding wound on the core. Since the initial pcrmeablity of the magnetic core material is negligible, the transformer would have negligible primary inductance or transformer coupling in the zero-field state and may be set into a condition of high primary inductance and close coupling by a coercive magnetic field above a certain strength generated by a control current in the auxiliary biasing winding initiated by the calling subscriber so as to interconnect the subscriber voice lines through an available crosslink circuit.

The various objects and features of the invention will be better understood from the following complete description thereof when it is read in conjunction with the several figures of the accompanying drawing, in which:

Figure 1 is a curve illustrating in idealized form the magnetization characteristics of the magnetic material used in the cores of the magnetic switching devices and systems embodying the invention;

Figures 2 to 5 respectively show schematic diagrams of a magnetic inverter, joint denial gate, AND gate and OR buffer embodying the invention; and

Figures 6 and 7 are schematic diagrams of magnetic switching devices comprising combinations of such inverter, gating and bufier circuits embodying the invention, respectively adapted for control switching and crosspoint switching in an electronic telephone switching office.

It is known that certain magnetic alloys have hysteresis loops that are unusually narrow near the origin, that is, they are constricted or wasp-waisted.

Figure 1 shows in somewhat idealized form the magnetization characteristic of one such alloy-65 Permalloy annealed in the absence of a field which is described on page 125 of the book Ferromagnetism by Richard M. Bozorth (published by Van Nostrand, 1951). This curve is a plot of induction or flux density (B), measured in gausses, against magnetic field strength (H), measured in oersteds. This curve is peculiar (but not unique) in that the remanent flux density is always very small compared to saturated flux density, and the permeability is negligible until a coercive magnetic field is applied to increase the permeability of the core material to a relatively high value. Referring to Figure 1, it will be assumed that the core material is initially not magnetized, that is, it is in the neutral state at the point designated 0. As a magnetic field of positive polarity is applied to the material in increasing strength, the fiux density within the material increases gradually to a point C for a given field strength and for field strengths above that value increases sharply to a point D representing positive magnetic saturation. .When the magnetic field is removed, the flux density drops as shown to the neutral point 0. When a magnetic field of the opposite (negative) polarity is applied to the core material, the flux density drops gradually down to the point B for a given field strength and for field strengths of greater negative value decreases sharply to the point F representing negative magnetic saturation. When the magnetic field is again removed, the flux density returns to the neutral point 0. Thereafter, as positive and negative magnetic fields are applied and removed, the flux density will vary over the paths traced above between the zero, and positive and negative magnetic saturation states. Thus, a core made from this material is suitable for use in a magnetic switch.

Figure 2 shows one magnetic switch arrangement in accordance with the invention that can be used as an inverter to give an output signal only in the absence of an input signal. As shown, it comprises a toroidal or ring core 1 made from a magnetic material having a wasp-waisted magnetization characteristic, such as 65 Permalloy annealed in the absence of a field, referred to above, and having an input winding 2, an output winding 3 and a magnetization control or clock winding 4 wound on different parts of this core. Its action may be described as follows:

(I) If there is no input pulse applied to the input winding 2, the effect of the clock pulse applied to the clock winding 4 on the magnetic core 1, referring to the curve of Figure 1, is to increase H past point C, so that there will be a change in a magnetic flux in the core material resulting in a corresponding pulse being generated in the circuit connected to the output winding 3;

(2) If an input pulse of the proper selected magnitude is applied to winding 2, the inductive elfect of the winding 2 will counteract the eiiect of the clock pulse on the core 1 to the extent that, referring to the curve of Figure 1, H never reaches the point C, there will be no change of flux in the core 1, and no signal pulse will be generated in the output circuit connected to output winding 3;

(3) At the end of a control pulse, the core 1, whatever its state of magnetization at the time, will return automatically to the neutral state 0 without the use of a demagnetizing force to accomplish this, and no holding power will be required to maintain it in this neutral state.

Figure 3 shows a modification of the switch arrange ment of Figure 2 in which two or more input windings 2a, 2b are provided on the core to enable two or more input signals of properly selected values to be applied thereto to produce an inductive effect on the core such as to prevent the core 1 from being activated by the clock pulse applied to the winding 4. Thus, this switch arrangement will produce an output signal in the circuit connected to the winding 3 only in the absence of any input signals applied to the input windings 2a, 2b and thus operates as a joint denial gate.

The switch arrangement of Figure 4 differs from that of Figure 3 only in the addition of means for inverting the input signals applied to the windings 2a, 2b as indicated in the figure by suitable labels. This may be accomplished, for example, by inserting an inverter such as illustrated in Figure 1 in each input circuit (not shown) or by any other suitable means. This modified switch arrangement with suitable modification of the magnetization control characteristics, such as the amplitude of the magnetizing pulses, may be made to operate as an AND gate to produce an output in the output winding 3 only when a signal is applied to each of the original inputs.

The switching arrangement of Figure 5 operates to give a final output in the presence of a signal in any one of the inputs, i.e., it will operate as an OR buffer. This arrangement comprises one magnetic switch component 5 equivalent to that of Figure 3, comprising a toroidal core 1a made from magnetic material having a waspwaisted magnetization characteristic, and four or more windings on this core including two or more input windings 2a, 2b an output winding 3a and a clock winding 4a, and a second magnetic switch component 6 equivalent to the inverter arrangement of Figure 2, having a toroidal core 1b made from the same magnetic material as core 111, and three windings on this core comprising one input winding 2c, one output winding 3c and one clock winding 4c. The output winding 3a of the switch 5 is connected through an intermediate circuit 7 to the input (intermediate) winding 20 of the device 6. A signal will be produced in the intermediate circuit 7 only in the absence of a signal in any of the input windings 2a, 2b and a signal will be generated in the output winding 30 only in the absence of a signal in the intermediate winding 2c, which occurs only when a signal is present in one or more of the input windings 2a, 2b

Figure 6 shows one arrangement for producing the control switching operations required in an electronic telephone switching office. It comprises three magnetic switch components 8, 9 and each including an identical core 1c made from the same magnetic material having a wasp-waisted magnetization characteristic such as shown in Figure l, and a plurality of control windings wound on each core. The portion of the switching arrangement formed by the switch components 8 and 9 in combination is equivalent to the OR butter arrangement of Figure 5, the component 8 having two input windings 2d and 2e, an output winding 3d and a clock winding 4d wound on its core; the component 9 having one input (intermediate) winding 2 one output winding 3 and one clock winding 4 wound on its core; and the output winding 30] of the component 8 being being connected through an intermediate circuit 11 to the input (intermediate) winding 2f of the switch component 9.

,The magnetic switch component 10 is similar to the Joint Denial Gate of Fig. 3, having five windings wound on its core 1c, two of which, 2g and 2h, are input windings, 3g is an output winding, 4g is a clock winding and 5a is an intermediate winding which is connected through a second intermediate circuit 12 to the output winding 3] of the switch component 9.

The switch arrangement of Figure 6 has two input circuits which will be referred to as IN-l and IN-2, the circuit LN-l being connected across one input winding 2d of switch component 8 and one input winding 2g of switch component 10 in series, and the circuit IN-2 being connected across the second input winding 2e of switch component 8 and the second input winding 2 h of switch component 10 in series. The combination switch arrangement has only one output circuit (OUT) connected across the output winding 3g of switch component 10.

The number and relative proportions of windings on the switch components 8, =9 and 10 and/or the characteristics of their associated circuits are selected to provide relative timing actions for these components such that when there is a signal in either input IN-l or lN-Z, the core 10 of magnetic switch component 9 is activated first under control of the clock pulse applied to its clock winding 4 resulting in signals being induced in the intermediate circuits 11 and 12 through its windings 2 and 31, respectively. In this condition, the cores 1c of switch components 8 and 10 are not activated, and no signal will be produced in the output winding 3g of switch component 10.

Where there is no input signal in either IN-l or IN-Z, the core 10 of switch component 10 will be activated first under control of the clock pulse normally applied to its clock winding 4g, causing a pulse to be produced in the intermediate circuit 12 through winding 5a. Then the intermediate pulse applied to the core 10 of switch component 9 through its winding 3] will be of sufiicient magnitude to counteract the effect of the normally applied clock pulse on the core of component 9, thus inhibiting that core so that no pulse will be generated in the intermediate circuit 11 through winding 2 Then, the core 10 of the magnetic switch component 8 will be activated under control of the clock pulse applied through the clock winding 4d so that there will be no net voltage produced across the input terminals of the magnetic switch component 10. The change in magnetization then produced in the core of component 10 under control of the clock pulse applied to its clock winding 4g will result in an output signal being induced in the output circuit of the combination arrangement through the output winding 3g.

In the switch arrangement of Figure 6 as described, undesired flow of information backward along the input lines due to current pulses induced in the input windings is eliminated. The fact that the arrangement of Figure 6 does not make use of diodes insures both long life and low power levels.

Figure 7 shows a basic schematic diagram illustrating the application of magnetic switching devices in accordance with the invention to cross-point switching in an electronic switching office of a voice telephone system. This diagram shows a four-line, two-link switching arrangement in which the horizontal lines designated L1, L2, L3 and L4 represent the two-wire voice lines of different telephone subscribers entering the ofiice and the lines designated K1 and K2 represent two-wire cross links utilized for providing the interconnections between the voice lines of different pairs of telephone subscribers to enable voice communication between them. To make such connections a plurality of automatic crosspoint switches respectively designated in the figure as CS1 to CS8 is utilized, one of these switches being located at each intersection between the lines L1 to L4 and the cross links K1, K2. When the switch at one of these intersections is in the closed condition the associated line and link are connected together electrically and when this switch is in the open condition they are not connected together electrically.

In accordance with the invention the crosspoint switches CS1 to CS8 are of the magnetic type each including as shown a toroidal or ring core MC made from a magnetic material, such as 65 Permalloy annealed in the absence of a field, having a wasp-waisted magnetization characteristic such as shown in Figure 1 of the drawings, and an input and an output winding forming a transformer and an auxiliary biasing winding respectively designated IW, OW and BW, wound on the core. As shown, the transformer input winding IW of each switch CS1 to CS8 is connected in circuit with a different one of the subscriber lines L1 to L4 and the output transformer winding OW of each switch is connected in circuit with the particular cross link K1, K2, at the intersection between this line and link. Since the initial permeability of the magnetic material of wasp-waisted characteristic in the magnetic core MC in each switch is negligible, the transformer formed by the windings IW and OW of each switch has negligible primary inductance or transformer coupling in the normal zero-field state so that each switch CS1 to CS8 is normally in the open condition effectively disconnecting the associated line and link from each other electrically. On the other hand, the transformer in each switch may be set into a condition of high primary inductance and close transformer coupling to operate the switch to the closed condition, by the application to the core CM of a coercive magnetic field H exceeding the value corresponding to the point C or E in the magnetization characteristic curve (Figure 1) of the core material. To make the desired connection between any two subscribers lines, control currents of suitable value are transmitted through the biasing windings BW of certain of the crosspoint switches CS1 to CS8 causing the application of the necessary coercive field to the cores thereof in order to operate these switches to the closed condition, by the operation of equipment (not shown) in the switching ofiice initiated by the voice currents of a calling subscriber requesting a particular connection.

Although only one magnetic alloy65 Permalloy annealed in the absence of a field-has been specified above for use in the magnetic cores of the switching devices in accordance with the invention, it is understood that any other suitable material having a wasp-waisted characteristic substantially as shown in Figure 1, may be used as a core material in these devices. Other changes in these devices which are within the spirit and scope of the invention will occur to persons skilled in the art.

What is claimed is:

1. A magnetic switching device comprising an input circuit adapted to be supplied at times with input signal pulses of given amplitude; an output circuit; a magnetic core made from a saturable magnetic material having a wasp-waisted type of magnetization characteristic in that its remanent flux density is at all times very small compared to its saturated flux density and its permeability is negligible until a coercive magnetic field of such strength as to drive the material to saturation is applied thereto; and a plurality of windings on said core including an input winding connected to said input circuit, an output winding connected to said output circuit, and a magnetizing winding supplied with magnetizing current pulses and responsive thereto to apply said coercive field to said core normal-1y causing the core material to be saturated and the core permeability to be increased to a relatively high value resulting in corresponding output signal pulses being induced in said output circuit through said output winding, the inductive effect of said input Winding in response to input signal pulses of said given amplitude applied thereto through said input circuit at said certain times serving to counteract the coercive field applied to the core by the magnetizing pulses thereby making the core permeability negligible and preventing the induction of the output signal pulses in said output circuit at such times.

2. A magnetic switching device comprising a magnetic core made from a saturable magnetic material having a Wasp-waisted type of magnetization characteristic in that its remanent flux density is at all times very small compared to the saturated flux density and its permeability is negligible until a coercive magnetic field above a given strength is applied to the material to drive it to the saturated condition; at least three inductive windings on said core including an input winding, an output winding, and a magnetizing winding supplied with magnetizing current pulses and responsive thereto to apply said coercive field to said core material; an input circuit connected to said input Winding and adapted to supply input signal pulses of given amplitude thereto during certain time intervals; and an output circuit connected to said output Winding; the change in magnetization produced by the coercive magnetic field in response to the supplied magnetizing pulses normally resulting in saturation of the core material and increase in its permeability to a relatively high value so that corresponding output signal pulses will be induced in said output circuit through said output winding, said input Winding operating in response to the input signal pulses of said given amplitude applied thereto through said input circuit during said certain time intervals to provide an inductive eifect counteracting the coercive field effect produced by said magnetizing pulses and, because of the resulting low permeability condition of the core material, will prevent the induction of output signal pulses in said output circuit during said time intervals, said core, regardless of the state of its magnetization, due to said magnetization characteristic of the material therein automatically returning to the unmagnetized state at the end of each applied magnetizing pulse and being maintained in this condition until the next magnetizing pulse is applied thereto.

3. A magnetic switching device comprising two or more input circuits respectively adapted to be supplied at certain times with input signal pulses of given amplitude; an output circuit; a magnetic core made from a saturable magnetic material the hysteresis characteristic of which is such that the remanent flux density is always very small compared to the saturated flux density and the permeability of which is negligible until a coercive magnetic field of a given strength sufficient to drive it to saturation is applied to the material causing its permeability to increase to a relatively high value; and a plurality of inductive windings on said core including two or more input windings respectively connected to a different one of said input circuits, an output winding connected to said output circuit, and a magnetizing winding periodically supplied with magnetizing pulses of such amplitude as to apply said coercive field to said core and normally causing output signals to be induced in said output circuit through said output winding due to the resulting high permeability condition of the core material; each of said input windings being proportioned so that its inductive effect on the core in response to applied input signal pulses of said given amplitude received through the associated input circuit at said certain times counteracts the inductive efiect thereon of the magnetizing winding under control of the applied magnetizing pulses and prevents the activation of the core to the saturated condition and thus induction of output signal pulses in said output circuit at said times, said device therefore operating as a Joint Denial Gate to generate output signal pulses in said output circuit only in the absence of any input signal pulses in said input circuits.

4-. The magnetic switching device of claim 3, in which said hysteresis characteristic of the magnetic material in said core insures that, regardless of its magnetization state at the time, the core at the end of each applied magnetizing pulse will automatically return to the neutral, unmagnetized state, and, without the use of any auxiliary holding power source, will be maintained in this neutral state until another magnetizing pulse is applied thereto.

5. The magnetic switching device of claim 3, in which means are provided for inverting the input signal pulses of said given amplitude applied through each input circuit to the associated input winding on said core and the coercive magnetic field applied by the magnetizing winding under control of the magnetizing pulses is made such that, when all the input windings are energized by applied signal input pulses, the inductive efiect of these windings in combination With the inductive effect of the energized magnetizing winding under control of the supplied magnetizing pulses causes said core to be activated to its saturated, high permeability condition and, when all of said input windings are deenergized with no input signal pulses applied thereto, the normal unsaturated, low permeability condition of said core is maintained, said device therefore operating as an AND gate to produce an output signal pulse in said output circuit only in the presence of an input signal pulse applied to the input of both of said input circuits.

6. A magnetic switching device comprising two switch components each including an identical magnetic core made from saturable magnetic material having hysteresis characteristics of the wasp-waisted type in that the remanent flux density thereof is always very small compared with the saturated flux density and its permeability is negligible until a coercive magnetic field of a given strength sufficient to drive the material to saturation is applied thereto, one of said components having two or more input windings, an output winding and a magnetizing winding wound on its core, the second switch component having one input winding, an output winding and a magnetizing winding Wound on its core, an intermediate circuit connecting the output Winding of said one component to the input winding of said second switch component, means for periodically applying magnetic pulses. to the magnetizing windings of the two switch components each of such amplitude as to cause a coercive magnetic field of said given strength to be applied to its core resulting normally in the core being driven to saturation with a resultant increase in its permeability to a relatively high value and the induction of corresponding output signals in the output Winding, an individual input circuit adapted to be supplied with input signal pulses of given amplitude connected to each input winding of said one switch component, and an output circuit connected to the output winding of said second switch component for receiving the output signals induced in that winding, the input winding of each component being proportioned so that its inductive efiect on the associated core in response to the input signal pulses of said given amplitude applied thereto through one of said input circuits or through said intermediate circuit will counteract the inductive effect on the core of the magnetizing winding of the component and prevent that core from being driven to saturation by the magnetizing pulses, said switching device therefore operating as an OR bufier to produce a signal pulse in said output circuit only in the absence of a signal pulse in said intermediate circuit which occurs only in the presence of an input signal pulse in one or more of said input circuits.

7. A magnetic switching system comprising three magnetic switch components each including an identical magnetic core made from saturable magnetic material having a wasp-waisted type of magnetization characteristic in that the remanent flux density therein is always very small compared to the saturated flux density and the permeability is negligible until a coercive magnetic field of a given strength is applied to the material to drive it to saturation; one of said switch components having an input winding, an output winding and a magnetizing winding on its core, the second of said components having two input windings an output winding and a magnetizing winding on its core and the third of said components having two input windings, an output winding, 2. magnetizing winding and an intermediate winding on its core; means for periodically applying magnetizing pulses to the magnetizing winding on the core of each of the three magnetic switch components of such amplitude that the resulting coercive fields applied to these cores is at least of said given strength which, because of the resultant increase in core permeability, would normally result in the induction of corresponding output signal pulses in the output Winding of each component; one intermediate circuit connecting the input winding of said one component to the output winding of said second component; a second intermediate circuit connecting the intermediate winding of said third component to the output winding of said one component, two input circuits respectively connected across one input winding of said second component and one input winding of said third component in series, and across the second input winding of said second component and the second input winding of said third component in series, each of said input circuits being adapted to be supplied at certain times with input sgnal pulses of a given amplitude; and an output circuit connected to the output winding of said third component; the relative proportions of the windings on the cores of the three switch components and the characteristics of their associated circuits being selected to control the relative timing actions of the three switch components such that when there is a signal pulse in any input circuit, the core of said one component is activated to the ln'gh permeability condition first causing the cores of the other two components not to be so activated because of the resulting signal pulses induced in the two intermediate circuits and no signal pulse will be produced in said output circuit; and when there is no input signal pulse in either input circuit, the core of the third component will be so activated first and the core of said second component second, resulting in the production of an output signal pulse in said output circuit.

8. In an electronic switching oflice of a two-way voice telephone system, including the terminating portions of the two-wire lines of a plurality of telephone subscribers and a plurality of two-wire cross links for use in providing connections between the lines of different pairs of telephone subscribers for two-way voice communication between these subscribers at the request of one of them, a magnetic switching system comprising a plurality of crosspoint switches respectively located at each intersection of a voice line and a cross link, each comprising a substantially identical magnetic core made from a saturable magnetic material having a magnetization characteristic of the wasp-waisted type in that its remanent flux density is always very small compared to its saturated flux density and its permeability is negligible until a coercive magnetic field of a given minimum strength is applied thereto, and a plurality of inductive windings on the core including an input and an output winding and an auxiliary biasing winding, the input and output winding of each switch being respectively connected in circuit with a subscriber line and a cross link and forming a transformer for coupling them at their point of intersection, this transformer, since the initial permeability of the associated core material is negligible, providing negligible primary inductance and thus transformer coupling between the associated line and link in the neutral unmagnetized state of the core material, thereby efiectively disconnecting this line and electrically from each other in this state, and said transformer when a coercive magnetic field of said given minimum strength is applied to its core being set into a condition of high primary inductance and close coupling to couple the associated line and link together electrically, and means under control of a calling subscriber to supply control current to the auxiliary biasing windings of selected ones of said switches of such values as to provide the coercive field of the necessary strength to the cores of these switches to operate them to the latter condition.

No references cited. 

